1. Field of the Invention
The present invention relates to a method of manufacturing a hose coupling fitting for connecting various kinds of hoses for fluids, such as automotive brake hoses.
2. Description of the Related Art
Conventional hose coupling fittings of this kind are furnished with a coupling head portion having a connection opening and a coupling body which has a nipple portion; a line on the brake cylinder side is connected to the connection opening, and a hose on the master cylinder side is inserted into and connected with the nipple portion to connect the master cylinder with the brake cylinder. In a hose coupling fitting of this design, the nipple portion is a thin elongated pipe which inserts into the path of the hose and which must be worked to high dimensional accuracy. For this reason the part is typically manufactured by a cutting operation, or by producing a separate component and unifying this with the coupling body by welding.
In this regard, with a view to manufacturing a hose coupling fitting of simpler design composed of single component without the need for a cutting process, methods which simply entail a series of cold forging steps have been considered; one such known technique is disclosed in JP 2002-361359 A. In this conventional technique, a large-diameter bore is formed in a thick, short rod-shaped material which then undergoes several cold forging steps to produce the connection opening and the nipple portion. However, in a conventional hose coupling fitting of ferrule shape having a socket portion and a nipple portion, appreciable deformation is necessary in order to transform the large-diameter through-bore into a narrow and elongated nipple hole, and it is difficult in practice for uniform shaping to take place between the upper end face and the lower end face of the nipple hole, thus creating the problem of appreciable deviation in the inside diameter dimension due to inside diameter taper or rippling, and making it difficult to achieve the desired shape.